1. Field of the Invention
The present invention relates to a driver for driving a semiconductor laser such as a laser diode.
2.Description of the Prior Art
Laser output vs. drive current characteristics of semiconductor lasers greatly vary according to their operating temperatures. More specifically, in order to obtain an identical laser output, a larger current is required at a high temperature.
In a conventional laser printer using a semiconductor laser as a laser source, if a laser output is not constant in the write mode, the image quality is degraded, thus posing problems in quality of recorded images.
For this reason, a conventional semiconductor laser driver is proposed wherein a laser output can be kept constant regardless of operating temperatures. This driver is called an APC (Automatic Power Control) circuit.
An example of the conventional semiconductor laser driver is constituted by a combination of an APC circuit for driving a semiconductor laser at a constant voltage and a semiconductor laser modulator.
In order to achieve temperature compensation in the constant voltage drive type APC circuit, a drive voltage for the semiconductor laser must vary according to an ambient temperature to keep the laser output constant. For this purpose, for example, an ambient temperature is detected and converted into an electrical signal and the drive voltage is then controlled in response to the cnverted electrical signal.
According to this technique, the temperature characteristics of the semiconductor laser must be checked in advance, and the corresponding control voltage must be generated. However, the characteristics of the individual semiconductor lasers vary and also change over time. Therefore, it is difficult to perform accurate temperature compensation.